This invention relates to a light emitting digital display and more particularly to such a display exhibiting high efficiency and producing high uniform brightness.
Available light emitting digital displays have digit scanning features for diminishing instantaneous power drain on miniature power sources. Power drain imposed on the power source by any digit depends upon the number of segments in the digit which are energized. In the usual display there are seven segments, which when all energized represent the arabic numeral 8. The minimum number of segments energized would be two, representing the arabic numeral 1. Different power drain levels occur between these two extremes for different symbols commanded from the normal seven segment dispLay. Differing power drain levels give rise to differing light intensity emission levels from the different digits. Different ambient light levels cause different display contrast levels and subsequent variation in display readability. Available light emitting digital displays attempting to cope with the problem of differing display readability in varying ambient light levels provide only stepped levels of display brightness, generally a low brightness level for low ambient light levels and a high brightness level for high ambient light levels. Such displays are limited in the degree of miniaturization wich may be achieved by the mechanical considerations for display actuating switches and display setting or adjustment switches.
A light emitting digital display and circuit for use therewith is needed which utilizes proximity sensing solid state switching circuitry together with circuitry for reducing the power drain from the miniature power source while providing high display luminous intensity, evenness of display brightness, and continuous contrast control relative to ambient light levels.